1. Field of the Invention
The present invention relates to a network monitoring system in which a master node and a plurality of slave nodes are connected in a ring-like manner by transmission lines, the master node and the plurality of slave nodes transmit state monitoring commands to monitor the network.
The present application is based on Japanese Patent Application No. Hei. 10-202159, which is incorporated herein by reference.
2. Description of the Related Art
The related network monitoring system is mounted in a vehicle, and this network monitoring system is configured such that a plurality of slave nodes, which include electrical equipment such as a radio, an amplifier, a compact disk player (hereafter referred to as the CD player), and a cassette, and a master node having an audio-visual controller (hereafter referred to as the AV controller) are connected in a ring-like manner by transmission lines. In such a ring-network monitoring system, communication using commands and data is mutually effected among the nodes, and the state of operation of the network is monitored.
As a method of monitoring the operational state by using the ring-network monitoring system, two monitoring systems are known, for example. The first monitoring system is shown in the flowchart in FIG. 6. In FIG. 6, a particular node, such as a central station, first sends a state monitoring command for monitoring the operational state of the network to all the other nodes (Step S101).
On the other hand, all the other nodes respectively determine whether or not the state monitoring command has been normally received (Step S103), and if that node has normally received the state monitoring command, that node transmits an affirmative response to the central station (Step S105).
Further, a determination is made as to whether or not processing has been executed up to the final node (Step S107), and if processing has not been executed up to the final node, the operation returns to processing in Step S101 and the processing in Step S101 and thereafter is repeatedly performed.
On the other hand, if the affirmative response is not transmitted from each node to the central station within a fixed period of time, the central station determines that the network is abnormal (Step S109).
Next, a second monitoring method is shown in the flowchart in FIG. 7. The network monitoring system based on this method is shown in FIG. 8. As shown in FIG. 8, a master node 103 and a plurality of slave nodes 105 are connected in a ring-like manner by transmission lines 101a to 101d, and data, commands, and the like are transmitted in the direction indicated by the arrows.
In FIG. 7, each of the nodes (slave nodes) waits for a fixed interval (e.g., 2 seconds) (Step S201), and transmits the state monitoring command to its immediate upstream-side node (Step S203). For instance, a slave node 105a transmits the state monitoring command to its immediate upstream-side master node 103 through slave nodes 105b and 105c (in the route indicated by the dashed line).
Next, the node concerned determines whether or not there has been an affirmative response from its immediate upstream-side node with respect to the state monitoring command (Step S205). For example, the slave node 105a determines whether or not there has been an affirmative response from its immediate upstream-side master node 103 (in the route indicated by the long dashed line). If there has been the affirmative response, a determination is made that the network is normal, and the processing ends.
On the other hand, if there has not been the affirmative response, a determination is made that an abnormality has occurred in a node or in the route of the network (Step S207).
However, with the related network monitoring system shown in FIG. 6, since the commands from the slave nodes are concentrated in a particular node such as the central station, the burden on the particular node has been large.
In addition, with the related network monitoring system shown in FIG. 7, each of the nodes transmits the state monitoring command irrespective of the amount of traffic on the network. For this reason, in an event that another command of a higher degree of importance has occurred, there has been a possibility that the state monitoring command serves as a hindrance to the command of the higher degree of importance.
Accordingly, it is an object of the present invention to provide a network monitoring system and a method thereof which are capable of monitoring the operational state of a network without causing a decline in the network efficiency.
To achieve the above object, according to the first aspect of the present invention, there is provided a network monitoring system which comprises at least one master node, a plurality of slave nodes controlled by the master node, wherein the master and slave nodes are connected in a ring-like manner through transmission lines, each of the nodes transmits data and commands in one direction through the transmission lines and transmits a state monitoring command for monitoring an operational state of a network to an immediate upstream-side node, and the operational state of the network is monitored by a response from the immediate upstream-side node with respect to the state monitoring command, a traffic monitoring unit provided in the master node, the traffic monitoring unit monitoring an amount of traffic in the network and determining whether the amount of traffic is less than a predetermined value, and a start-command transmitting unit provided in the master node, the start-command transmitting unit transmitting a start command for instructing a start of transmission of the state monitoring command to each of the slave nodes when the traffic monitoring unit determines that the amount of traffic is less than the predetermined value.
In accordance with the first aspect of the present invention, the traffic monitoring unit monitors the amount of traffic in the network and determines whether or not the amount of traffic is less than a predetermined value, and the start-command transmitting unit transmits a start command for instructing the start of transmission of the state monitoring command to each of the slave nodes if it is determined that the amount of traffic is less than the predetermined value.
Namely, since the state of the network is monitored when the amount of traffic in the network is at a predetermined value, e.g., zero, it is possible to monitor the operational state of the network without causing a decline in the network efficiency.
According to the second aspect of the present invention, preferably, each of the slave nodes has a position, information unit managing relative position information that indicates order of a position of the node from the master node.
In accordance with the second aspect of the present invention, the slave node concerned is able to easily ascertain the order of the position of that node from the master node, on the basis of the relative position information managed by the position information unit.
According to the third aspect of the present invention, preferably, each of the slave nodes has a state-monitoring-command transmitting unit transmitting the state monitoring command at a command transmission time related to the relative position information of the position information unit, on the basis of the start command received from the master node.
In accordance with the third aspect of the present invention, the state-monitoring-command transmitting unit transmits the state monitoring command at a command transmission time related to the relative position information of the position information unit. Namely, since the slave nodes transmit the state monitoring commands at mutually different times, it is possible to avoid collisions between the state monitoring commands of their own nodes and the state monitoring commands of the other nodes.
According to the fourth aspect of the present invention, there is provided a network monitoring method. In the network monitoring method, first, at least one master node and a plurality of slave nodes controlled by the master node are provided. The master node and the slave nodes are connected in a ring-like manner through transmission lines, each of the. nodes transmits data and commands in one direction through the transmission lines and transmits a state monitoring command for monitoring an operational state of a network to an immediate upstream-side node, and the operational state of the network is monitored by a response from the immediate upstream-side node with respect to the state monitoring command. Further, the master node is caused to monitor an amount of traffic in the network and determine whether the amount of traffic is less than a predetermined value. Still further, the master node is caused to transmit a start command for instructing a start of transmission of the state monitoring command to each of the slave nodes when the master node determines that the amount of traffic is less than the predetermined value.
According to the fifth aspect of the present invention, preferably, the network monitoring method further comprises a step of causing each of the slave nodes to manage relative position information indicating order of a position of the node from the master node.
According to the sixth aspect of the present invention, preferably, the network monitoring method further comprises a step of causing each of the slave nodes to transmit the state monitoring command at a command transmission time related to the relative position information, on the basis of the start command received from the master node.